1. Field of the Invention
The invention is directed to a system and methods for transmitting/receiving data during Broadcast mode and Multicast mode and, more particularly, to a method for minimizing signalling loads due to mutual exchanges of information between neighboring cells in which a session is transmitted, and for reducing a time required to transmit MBMS neighbor cell information messages in a serving cell when a higher level of signalling occurs.
2. Detailed Description of the Related Art
MBMS (Multimedia Broadcast/Multicast Service) is a unidirectional Point-to-Multipoint (p-t-m) multicast/broadcast service in which data is transmitted from a single source entity to a group of users located in a specific area. MBMS may comprise a selection of unidirectional p-t-m bi-directional point-to-point (p-t-p) transmissions of multimedia data, such as text, audio, picture, or video, from a single source entity to a multiplicity of users in a service area. As stated in the 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 22.146, “Multimedia Broadcast/Multicast Service; Stage 1”, it is a goal of MBMS is to allow the provision of multiple instances of a p-t-p service with a single transmission over a radio interface as a radio multicast. “Service area” for a given MBMS service is hereafter to be understood as the geographical area (i.e. set of cells) where the service is made available.
MBMS has two modes, e.g., Broadcast mode and Multicast mode. The main difference between these two modes is that in Broadcast mode all MBMS users in the service area are targeted for receipt of transmitted data, whereas in Multicast mode it is possible to address only a subset of the MBMS users in the service area for receipt of the data. As defined in the 3GPP TS 22.146, “Multimedia Broadcast/Multicast Service; Stage 1,” Multicast mode typically requires a user to subscribe to a multicast group before receiving the service.
In GP-042013 “Assisted Cell Change during MBMS p-t-m Transmission”, Siemens, Telecom Italia S.p.A, Vodafone, 3GPP TSG GERAN#21 (Montreal, Canada), a solution is described for providing a source cell with the information about the MBMS bearer (p-t-m channel) in the neighboring cells for a given session. With reference to FIG. 1, it is optimal if a mobile station (MS) can resume reception of MBMS data in the target cell as soon as a new cell has been selected, during acquisition of Packet-Broadcast Control Channel (P-BCCH) information, or during a Routing Area Update procedure.
MBMS traffic channel configuration and MBMS service ID information is sent via an existing Radio Link Control/Medium Access Control (RLC/MAC) message, such as a conventional packet neighbor cell data (PNCD) message that is used to convey neighboring cell system information in a serving cell. Alternatively, the MBMS traffic channel configuration and MBMS service ID information is sent in a new message that is transmitted on a packet associated control channel (PACCH) that is associated with the MBMS traffic p-t-m channel. A new message is defined herein as MBMS neighbor cell information, whether it is a PNCD message or a new message.
MBMS neighbor cell information (Cell C, Session S) refers to an MBMS neighbor cell information message that contains at least: i) the parameters that permit identification of and access to the neighboring cell C; (ii) the parameters of the MBMS bearer (p-t-m channel) on which the session S is transmitted in cell C; and/or (iii) an identifier of the session S. This information is transmitted for the following reasons: (i) as a way to provide the users with available information as soon as possible, subsequent to commencement of the MBMS data transfer in the serving cell; (ii) when the MBMS bearer (p-t-m channel) is reconfigured or an initiation of the new MBMS service in a specific neighboring cell has occurred. In this case, the base station controller (BSC) broadcasts the new bearer configuration on the packet associated control channel (PACCH) in the specific neighboring cell; (iii) when periodic repetitions of the information is required in order for mobile stations (MS) (e.g., mobile phones, PDA, etc.) entering the cell (e.g. late arrivals) to acquire the information; and (iv) when a repetition of the information is further required to account for possible errors on an air interface.
The main problem associated with the conventional method for receiving data during Broadcast mode and Multicast mode is the high level of signal loading that is triggered by the mutual exchange of information between neighboring cells in which the same session is being transmitted. This signalling load not only comprises the applicable signalling load between BSCs, but more importantly it comprises the signalling load on the air interface of each cell. This leads to an overall reduction in system performance and data throughput. For example, if a session S is ongoing in a given cell A, and if the same session S is ongoing in a cell B neighboring cell A, then the parameters of the p-t-m information for session S in cell B must be sent in cell A, and the parameters of the p-t-m information for session S in cell A must also be sent in cell B. In other words, MBMS neighbor cell information (Cell A, Session S) must be sent in Cell B, and MBMS neighbor cell information (Cell B, Session S) must be sent in Cell A. This principle applies to every single ongoing session in any given cell, for all 4 cases where information is transmitted, as listed above.
Another problem associated with receiving data during Broadcast mode and Multicast mode, which is also implied by the problem described above, is that the higher the amount of signalling (i.e. the higher the amount of neighboring cells and the amount of ongoing sessions both in the serving cell and one or more of its neighboring cells), the longer the time it takes to send all the necessary MBMS neighbor cell information messages in the serving cell. As a result, a mobile station (MS), i.e. an MS that is in motion, has a lower probability of receiving the p-t-m information for the cell into which it is moving prior to reselecting the new cell. Thus, the utility associated with transmitting neighboring cell information in broadcast mode or multicast mode becomes jeopardized.
Accordingly, there is a need to minimize the signalling load due to mutual exchanges of information between neighboring cells in which the same session is being transmitted, and to reduce the time required to send MBMS neighbor cell information messages in a serving cell when a higher level of signalling occurs.